An integrated circuit often contains output drivers coupled to a bus, where the output drivers provide an output voltage signal carried by the bus that meets specified amplitude and rise time requirements. Output pads, coupled to an integrated circuit and used as a connection point to output signals of the integrated circuit, have very basic pre-driver and drivers that turn on or control a single or multiple leg design in order to control the rise time of an output voltage signal. The bus coupled to the output driver may be a terminated or unterminated bus. More complex output pads may turn on FET legs with a delay loop or control circuitry, which can be viewed as switching resistors into the bus.
This approach is less effective on un-terminated buses. If the output driver is not controlled, the resulting voltage spike may impact the bus coupled to the output driver. The voltage spike can create ringing and signal integrity issues on a signal carried by the bus. More complex pads don't drive the bus signal to specific voltage levels—but instead control switching of FET legs of the driver.